This laboratory has at hand five purified invertebrate muscle lactate dehydrogenases of differing lactate stereospecificity and subunit association: Limulus polyphemus (horseshoe crab): D-lactate, dimer; Hormarus americanus (lobster): L-lactate, dimer reversibly yields tetramer; Balanus nubilus (barnacle): D-lactate, tetramer; Helix aspersa (garden snail): D-lactate, dimer reversibly yields tetramer; Haliotus cracherodii (abalone): D-lactate, dimer reversibly yields tetramer. The first three of the above list have been extensively characterized. A major aspect of the proposed work is the catalytic and physico-chemical characterization of the remaining two molluscan D-lactate dehydrogenases, particularly regarding the nature of subunit association. The degree of homology, evolutionary relatedness, and the nature of subunit conformations and association for the above five enzymes are being studied by the use of analytical ultracentrifugation, CD-ORD and fluorescent spectroscopy, reversible subunit dissociation (hybridization), and amino acid sequencing. Efforts will also be made to isolate a representative L-lactate dehydrogenase from the phylum echinodermata.